Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$170.81	11.371%	$190.2328	$190.23	$190.25	$190.20
Purchase #2	$114.85	7.219%	$123.141	$123.14	$123.15	$123.10
Purchase #3	$35.58	8.797%	$38.71	$38.71	$38.70	$38.70
Purchase #4	$117.32	13.625%	$133.3049	$133.30	$133.30	$133.30
Purchase #5	$134.28	9.861%	$147.5214	$147.52	$147.50	$147.50
Purchase #6	$168.90	10.577%	$186.7646	$186.76	$186.75	$186.80
Purchase #7	$150.55	9.473%	$164.8116	$164.81	$164.80	$164.80
7 purchase totals =	$892.29		$984.4863	$984.47	$984.45	$984.40